The present invention relates to an exhaust gas recirculation (EGR) system for returning part of exhaust gas of an engine to an intake system to improve the fuel efficiency and exhaust performance.
In order to improve fuel consumption for less CO.sub.2 and to lower the combustion temperature for less NOx in compliance with growing environmental concerns, there have been proposed a variety of EGR systems for recirculating a controlled amount of exhaust gas to the intake system in a normal operation not requiring higher output power.
Japanese Utility Model Kokai Publication No. 3(1991)-114563 shows a first conventional EGR system having a horizontally confronting pair of openings for introducing EGR gas into an intake pipe. Japanese Utility Model Kokai Publication No. 3(1991)-114564 shows a second conventional EGR system having an annular EGR gas passage around an intake pipe and a plurality of holes for introducing the EGR gas from the annular passage into the intake pipe. Both systems are aimed to reduce the cylinder to cylinder nonuniformity in the EGR rate.
Japanese Patent Kokai Publication No. 8(1996)-218949 discloses a third conventional EGR system having an EGR passage opening to a second surge tank provided downstream of a first surge tank in an intake passage. This system introduces the EGR gas at a remote position from a throttle valve, to prevent adhesion to the throttle valve, of harmful components (deposits) of the exhaust gas mixture.
Japanese Utility Model Kokai Publication No. 60-171952 discloses a fourth conventional EGR system having an EGR pipe connected, through an EGR valve, to a surge tank of an intake manifold.